Dr. Conrad MurrayJailmates with Michael Jackson'sEx Brother-in-Law

2/6/2012 6:00 AM PT

EXCLUSIVE

There are nearly 4,000 inmates at L.A. County Men's Jail, so imagine the coincidence that Dr. Conrad Murray is in a cell just feet away from Michael Jackson's former brother-in-law.

James DeBarge -- Janet Jackson's ex-husband -- is locked up after being arrested for assault with a deadly weapon and drug charges. DeBarge -- who was the lead singer of the wildly popular band, DeBarge -- has been placed in Administrative Segregation -- the place where famous inmates with security issues are housed.

Murray has been calling the Ad Segregation unit home since his conviction on manslaughter charges last November.

We're told they occasionally run into each other, most recently last Monday when they were each meeting with their respective lawyers in the visiting room.

DeBarge's lawyer, Spencer Vodnoy, tells TMZ ... the singer is "really upset" he's so close to Murray. DeBarge says even though he was married to Janet for less than a year back in '84, he thought of Michael as a brother.